The fluid catalytic cracking (FCC) process has been in operation for over 50 years and has gone through many changes. These changes have been in the well-known catalyst and additives employed in the process, as well as mechanical and process changes. In the last decade there has been a slow but constant pressure and realization that proper FCC catalyst management can result in a significant reduction in the FCC operating costs and improved FCC operating stability.
A first significant disclosure for improved FCC catalyst management was disclosed in my European Patent Application No. 0 408 606 B1 “Fluid Catalytic Cracking (FCC) Catalyst and Additive Loading Control System” and in the Bartholic, Lippert U.S. Pat. No. 5,389,236 “Method and Apparatus for Controlling Introduction of Catalysts into FCC Units”, which are incorporated by reference in their entirety in this application. These two publications disclose an improved method for adding fresh FCC catalyst and FCC additives to an FCCU. Refiners who have employed these systems have noted improvements in the operating stability of their FCC unit (FCCU) and reduced catalyst/additive usage, which translates into reduced unit operating costs, and more on-specification products. The use of these systems for FCC additive addition has been widely employed. However, the use of these systems for fresh catalyst addition has not been widely accepted, because it requires a fairly large capital expenditure and replacement of the existing fresh catalyst storage hopper of the FCCU.
In my U.S. Pat. No. 5,888,919 “Process for Zeolitic Catalyst Reactivation” and the Bartholic, Davis U.S. Pat. No. 5,900,383 “Process for Increasing the Activity of Zeolite Containing Particulate Solids”, which are incorporated by reference in their entirety in this application, there are disclosed processes which enable for the reuse of FCC equilibrium catalyst by increasing the equilibrium catalyst activity through forming what is referred to herein as “reactivated FCC equilibrium catalyst”.
There are also well-known processes for removing deposited metals, primarily Ni and V, from equilibrium catalyst to form what is referred to herein as “demetalized equilibrium FCC catalyst”. One such process, known as DEMET, was originally developed by ARCO in the 1950's and 1960's to remove metals from high aluminia FCC equilibrium catalyst. This process was further developed to remove metals from zeolitic FCC equilibrium catalyst. An improved DEMET process is described in U.S. Pat. No. 4,686,197, which is incorporated herein by reference. More recently, Coastal Corporation, has further refined this process to remove metals (demetalization) and increase the activity (reactivation) of zeolitic catalyst. This latter process is referred to as the ACT Process and is described in U.S. Pat. No. 6,046,125, which is incorporated herein by reference. It should be noted that demetalization refers to the removal of one or more metal elements that are deposited on the catalyst from the feed and are considered to be detrimental to the FCC catalyst activity or yield structure of the product of the process. Among these metals are Ni, which increases hydrogen production, and Na and V, which are also detrimental to catalyst activity.
Up until now, the typical refiner has added fresh catalyst and additives to maintain the desired catalyst activity in the FCCU and has withdrawn excess equilibrium catalyst to maintain the desired unit inventory. In an FCCU, I estimate that only about 30%, more or less, of the circulating catalyst inventory has a substantial catalytic activity. The other 70 wt %, more or less, is relatively catalytically inert. Of the 30% active material, the activity of the circulating catalyst particles ranges from a high of fresh catalyst activity to very low activity. If one uses an activity test unit to quantify the activity (defined as conversion to lower molecular weight hydrocarbons of a standard gas oil feed in the activity test unit divided by the quantity {100−[conversion in the activity test unit]}), the circulating catalyst inventory in a typical FCCU might have an activity of 2.33 (for 70% conversion in activity test unit; i.e., 70/100−70=2.33). The fresh catalyst activity might be 13.28 (for 93% conversion) or 5.7 times as active as the circulating catalyst inventory, which is sometimes referred to equilibrium catalyst or ECAT. The inert catalyst particles in the circulating catalyst inventory might have an activity of 0.33 (for 25% conversion). More importantly, if one compares the coke yield on the activity test for these activity ranges, one might find the coke yield for the fresh catalyst to be 3 to 5 times higher than the coke yield on the ECAT. This is important since it limits the zeolite content of fresh FCC catalyst to about 15-30% in the typical FCCU.
Because of environmental concerns and disposal costs, most refiners withdraw a minimum of equilibrium catalyst from their units. In this case, the fresh catalyst added to the FCCU is typically selected and added to maintain a desired yield structure and unit activity and to make up for unit catalyst losses through the cyclones of the FCCU.
Equilibrium catalyst or ECAT is defined as the catalyst that is circulating in the FCCU and consists of the fresh FCC catalyst and FCC additives which were just added to the unit plus the FCC catalyst and FCC additives which have made more than one cycle between the reactor and the regenerator of the FCCU and are less active than the fresh catalyst and additives. In those units that process feedstocks which contain metals and other catalyst poisons the equilibrium catalyst also has thereon metals and poisons deposited from the feedstock.
Some refiners processing high quality feeds (containing low metals and catalyst poisons) may elect to add more fresh catalyst than the amount lost from the unit. Therefore, they will withdraw ECAT that is usually of high quality (low metals, higher than normal activity) that they will then sell to operators of units which process residual oil or might be experiencing a high catalyst loss problem. This high quality ECAT is typically sold at less than 50% of the fresh catalyst selling price.
Units processing residual oil that contains metals, such as Ni, V, and Na, and other catalyst poisons in excessive amounts will require that the refiner add fresh catalyst or high quality ECAT to maintain the unit ECAT activity and metals level at some predetermined value that will give the desired unit yield structure and profitability. In this case, usually the amount of catalyst addition is more than the catalyst losses from the unit, so the refiner must remove ECAT from the unit for disposal. Since this ECAT is of poor quality, the refiner must pay for its disposal.
In a typical FCCU adding fresh catalyst, a large percentage (30-70%) of the fresh catalyst is lost through the cyclone system of the unit. The majority of the initial loss is the catalyst fines and moisture contained in the fresh catalyst, plus some loss by attrition. The rest of the loss of catalyst from the unit is mainly equilibrium catalyst and the amount varies with the cyclone efficiency, because the cyclones are less than 100% efficient in separating the catalyst from the vapors. In FCC units that have metals in the feed, the type and quantity of catalyst addition will be determined to control both the equilibrium catalyst activity/selectivity and level of metals deposited on the catalyst. Some refiners have added purchased equilibrium catalyst to their unit to control the unit inventory, selectivity, metals level and/or activity of the circulating catalyst inventory (note: ECAT losses are considerably less than that of fresh catalyst, since the ECAT has very low fines and moisture content and low attrition). Typically, these refiners will purchase low metals equilibrium catalyst with an activity equal to or greater than the catalyst activity in their units and add this purchased ECAT in place of fresh catalyst addition.
Up until now, because of limitations in FCCU catalyst hopper/storage capacity to segregate catalyst types, the typical refiner has usually been restrained to the use of one fresh FCC catalyst or one outside supply of FCC ECAT that is added from the fresh catalyst storage hopper of the FCCU. That is, the typical FCCU has one fresh storage hopper and one equilibrium storage hopper. Therefore, if the refiner purchases FCC ECAT from an outside source, he must use the fresh catalyst storage hopper to add this material. If he adds this outside-purchased material to the ECAT storage hopper, there will be cross contamination with the unit's ECAT when unit ECAT is withdrawn to maintain unit inventory or during a shutdown, when the unit inventory is removed from the unit to the ECAT storage hopper. If the refiner wants to add both fresh and outside ECAT to his unit, then he must install another addition hopper for this outside ECAT.
As the number of catalyst additives, fresh catalyst, and equilibrium catalyst employed in the FCCU increases, the number of hoppers for catalyst addition and catalyst storage increases, and the catalyst management associated with this part of the FCCU operation takes up more and more time and resources. Every time a new catalyst, fresh or equilibrium, or catalyst additive, arrives at the refinery, it must be weighed on the refinery scale, the hopper must be inventoried by transferring from the truck, rail car, or container. This transfer requires depressuring the existing hopper, pulling a vacuum on the hopper, connecting the truck, rail car, or container to the hopper, connecting up pressuring air and conveying air, and manually regulating the transfer of the material into the hopper. After the transfer is complete, the hopper must be pressured and placed back in service, and the above procedure reversed so that the truck, rail car, or container can be weighed to determine the amount of catalyst delivered. Given the size of the equipment involved, this procedure may take eight hours or more, and ties up personnel that have other duties.
The present invention concerns a method which improves catalyst management so as to reduce the associated time required by the refinery personnel. The present invention also reduces the overall catalyst costs. A further objective of the present invention is to reduce catalyst transportation costs. Also, the present invention enables the refiner to form an alliance with a single catalyst supplier, who would supply all the refiner's requirements for fresh, equilibrium, demetalized, and reactivated FCC catalyst and FCC additives. This is especially useful as more and more consolidation in the refining industry occurs. Another object of this invention is to utilize the weigh scale function as described in U.S. Pat. No. 5,389,236 to supply signals to an offsite location that can monitor the FCC unit inventory of fresh catalyst and additives. In this way, the refiner can maintain minimum FCC catalyst inventory (lower cost) and the supplier can deliver product only when required. Another object of the present invention is to provide the refiner with the ability to select from a multiple of sources (fresh, reactivated ECAT, demetalized ECAT, additives) for the FCCU “fresh catalyst” (hereinafter referred to as “intermediate fresh catalyst” or, IFC) that will result in the desired unit yield structure and activity at the lowest possible price. Still another object of the present invention is to reduce the refiner's capital requirements, in that he will not be required to add more hoppers or build on-site demetalization or reactivation systems. In addition, this invention enables reuse of ECAT, which will result in the use of less raw materials and energy, reduce unit catalyst losses, result in a higher unit activity than an equivalent fresh catalyst, since more of the ECAT will remain in the unit compared to fresh catalyst, and result in less disposal to landfill.